The postmortem activation status of platelets.

Platelets are activated by substances from the subendothelial matrix in endothelial lesions or by factors in the plasma coagulation cascade. Conversely, activated platelets are potent activators of this cascade. Only activated platelets express the adhesion molecules Gp53, GMP140 and thrombospondin on the plasma membrane. The postmortem activation status of platelets, therefore, can be determined immunoelectron microscopically by immunogold labeling of antibodies against these glycoproteins. Our studies revealed that the vast majority of these antigens were located within the granules postmortem, hence the platelets had not been activated. Thrombin-induced activation of platelets in vitro was only possible in the early postmortem interval, as demonstrated by labeling of the adhesion molecules on the plasma membrane. Later, such activation was no longer possible even though thrombin-induced fibrin formation gave the appearance of "coagulated blood". In forensic medicine, these findings can possibly be applied to distinguish intravital clotting from the postmortem coagulation phenomena and intravital hematomas from postmortem hematomas.